Method for controlling of a pump unit and a pump unit for pumping liquid or suspension

Abstract

A method for controlling a pump unit for pumping liquid or suspension includes controlling a pump unit based on a determination of a combination of an inducer and a centrifugal pump at least on parameters of a total volumetric flow rate and pressure difference over the pump unit, and controlling the pump unit based on a rheology of a fluid to be pumped so that necessary fluidization parameters of the fluid are predetermined to enable operation of the pump unit, and the rotation speed of the inducer rotor or an output power of the inducer rotor is controlled to a desired volumetric flow rate.

1 . A method for controlling a pump unit for pumping liquid or suspension, the pump unit comprising a centrifugal pump and an inducer in a proximity upstream of an inlet ( 210 ) of the centrifugal pump,
 the centrifugal pump comprising a pump housing forming a flow channel inside the pump housing and an impeller configured to be rotated in the flow channel around a central axis by a shaft,   the inducer comprising an inducer rotor having a sleeve-shaped rotor body, the inducer rotor is configured to be rotated around the central axis in the flow channel, the rotor body including a number of blades extending inwards from the rotor body,   the inducer rotor being is separate to the impeller and a rotation speed of the inducer rotor is independently controlled in relation to a rotation speed of the impeller, the inducer comprising an electric motor that is an annular motor encircling and connected to the inducer rotor, the method comprising:   controlling of the pump unit based on a determination of a combination of the inducer and the centrifugal pump at least on parameters of a total volumetric flow rate and pressure difference over the pump unit, and controlling the pump unit based on a rheology of a fluid to be pumped so that necessary fluidization parameters of the fluid are predetermined to enable operation of the pump unit, and the rotation speed of the inducer rotor or an output power of the inducer rotor is controlled to a desired volumetric flow rate.   
     
     
         2 . The method according to  claim 1 , wherein the pump unit is controlled based on the rheology of the fluid to be pumped so that a calculated Power number—Reynolds number—curve is used as a reference curve to control the rotation speed of the inducer rotor or an output power to operate the pump unit at a desired operational window. 
     
     
         3 . The method according to  claim 1 , wherein the pump unit is controlled so that the output power of the inducer rotor is less than an output power of the centrifugal pump. 
     
     
         4 . The method according to  claim 1 , wherein, wherein the rotation speed of the inducer rotor is controlled based on detected cavitation at the centrifugal pump, and a head generated by the inducer is increased or decreased to maintain a margin to an outbreak of cavitation of the impeller. 
     
     
         5 . The method according to any of  claim 1 to 3 , wherein an NPSHaB (Net Positive Suction Head Available at the inlet of the impeller) is measured, calculated or otherwise determined, and the rotation speed of the inducer rotor or a head of the inducer is driven along a predetermined NPSHr (NPSH required) curve for a given operation condition. 
     
     
         6 . The method according to  claim 1 , wherein the rotation speed of the inducer rotor or the output power of the inducer rotor is controlled based on required gas separation for given-a fluid to be pumped, the required gas separation determinable based on gas detection or predetermination to determine a gas content in the fluid. 
     
     
         7 . A pump unit for pumping liquid or suspension, the pump unit comprises:
 the centrifugal pump comprising the inducer in the proximity upstream of the inlet of the centrifugal pump:   the centrifugal pump comprising the a pump housing forming the flow channel inside the pump housing and the impeller configured to be rotated in the flow channel around the central axis by a shaft,   the inducer comprising the inducer rotor having the sleeve-shaped rotor body, the inducer rotor is configured to be rotated around the central axis in the flow channel, the rotor body includes the number of blades extending inwards from the rotor body,   the inducer rotor is separate to the impeller and the rotation speed of the inducer rotor is independently controllable in relation to the rotation speed of the impeller, the inducer comprising the electric motor that is the annular motor encircling and being connected to the inducer rotor,   the pump unit connected to a controller configured to execute the method of  claim 1  such that the pump unit is controlled based on the rheology of the fluid to be pumped so that necessary fluidization parameters of the fluid are predetermined to enable operation of the pump unit, and the rotation speed of the inducer rotor or the output power of the inducer rotor is controlled to the desired volumetric flow rate.   
     
     
         8 . The pump unit according to  claim 7 , wherein the inducer rotor and impeller are drivable by separate electric motors electrically connected to the controller. 
     
     
         9 . The pump unit-according to  claim 7 , wherein the inducer rotor is rotatable to an opposite or to a same direction as the impeller. 
     
     
         10 . The pump unit  according to 7 , wherein the inducer-comprises an inlet, an inducer housing to enclose a stator, an annular motor and the inducer rotor, the inducer housing being connected to the pump housing via a flange attachment at a distance from 0.01 up to 10 times a diameter of the flow channel. 
     
     
         11 . The pump unit  according to 7 , wherein guide vanes are disposed between the inducer and the impeller, the guide vanes having a fixed or adjustable pitch. 
     
     
         12 . The pump unit according to  claim 11 , wherein the guide vanes-comprise conduits for gas removal from the liquid. 
     
     
         13 . A pump unit  according to 7 , wherein the rotation speed of the inducer rotor is variably or independently controllable in relation to the rotation speed of the impeller. 
     
     
         14 . The pump unit of  claim 7 , further comprising at least one sensor of the following sensors to monitor the centrifugal pump or to determine NPSHaA (Net Positive Suction Head Available at the inlet of the inducer) or NPSHaB values: a pressure sensor, an acoustic sensor for cavitation monitoring, a vibration monitoring sensor, an on-line consistency sensor, an on-line gas content meter, or a thermometer. 
     
     
         15 . The pump unit of  claim 7 , further comprising a device configured to monitor the centrifugal pump calculations using software of variable speed drive. 
     
     
         16 . A controller for controlling the pump unit according to  claim 14 , the controller comprising executable instructions to control the rotation speed of the inducer rotor or the output power of the inducer rotor based on a sensor signal of the at least one sensor such that the pump unit is controlled based on the rheology of the fluid to be pumped so that the necessary fluidization parameters of the fluid are predetermined to enable operation of the pump unit, and the rotation speed of the inducer rotor or the output power of the inducer rotor is controlled to a desired volumetric flow rate.